The present invention relates to cutting tools used to cut through soft ground or through relatively soft material that has been laid on the ground, such as asphalt roadways.
Mining, excavating, and road resurfacing operations are typically performed by forcing rotary cutting bits through the material being cut. The cutting bits are mounted on a driven support, such as a rotary drum, fixed beam, or the like to be forced through the material. A typical cutting bit comprises a hard cemented carbide tip that is brazed to the front surface of a steel shank. The shank is to be mounted in a holder by means of a retainer sleeve which permits the bit to rotate freely relative to the holder about the bit's center axis, while being restrained against axial dislodgment from the holder. Due to being freely rotatable, the tip is basically self-sharpening.
It should be understood that cutting mechanisms of the type described above have been used to cut through hard materials, such as rock and ice, in addition to cutting through softer materials such as asphalt. During the cutting of rock, the highest rate of bit wear occurs at the carbide tip, so the wear life of the bit is determined by the carbide tip. However, during the cutting of relatively softer material, such as asphalt, coal, and salt, the highest rate of wear occurs at the shank, i.e., erosion caused by cut asphalt rubbing and impacting against the shank. Thus, when cutting asphalt during a road resurfacing operation, the wear life of the cutting bit is determined by the shank.
It would be desirable to provide a cutting bit that has an increased wear life when used for cutting softer materials such as asphalt.
Disclosed in U.S. Pat. No. 4,725,098, which is incorporated by reference, is a cutting bit in which a groove is machined in a tapering side surface of the bit head closely behind a carbide tip mounted in the bit head. Hardfacing is deposited into the groove to form an erosion-resistant annular ring which can be flush with, or project slightly radially beyond, the side surface. Despite being formed of hard material, the ring will be subjected to considerable erosion by cuttings and thus will have a somewhat limited life.
U.S. patent application Ser. No. 10/058,387, filed Jan. 30, 2002, entitled Rotary Cutting Bit with Material-Deflecting Ledge, naming Kent Peay and Timothy J. Shean as inventors, and now U.S. Pat. No. 6,709,065 which is incorporated by reference, discloses a cutting bit having a tapered side surface with a ledge projecting from the tapered surface. The ledge can be integral with the rest of the bit body or formed as a separate ring held on the body. The ledge is of sufficient diameter relative to the portion of the body above it that material cut tends to accumulate on the ledge and shields the body material underneath from erosion. However, it has been found that the ledge in such a cutting bit is highly prone to wear.
It would be desirable to provide a cutting bit with an erosion-resistant structure which has an enhanced life. It would also be desirable to provide a cutting bit that is simple to manufacture and involves relatively few manufacturing operations.
In accordance with an aspect of the present invention, a cutting bit includes a body having a front surface and a side surface, the side surface including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, the body being no larger in diameter above the shoulder than at the shoulder, and a ring that is harder than the body attached to the body at a front surface of the shoulder.
In accordance with another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A distance between the front surface and a top of the ring divided by a distance between the front surface and a bottom surface of the body is 0.15 to 0.5.
In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, a cutting tip attached to the front surface, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A diameter of a bottom of the cutting tip divided by the diameter of the body at the bottom of the cutting tip is 0.72 to 0.95.
In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, a cutting tip attached to the front surface, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A diameter of the cutting bit divided by an outside diameter of the ring is 0.60 to 0.80.
In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a side surface, the side surface including a first shoulder below the front surface and extending substantially perpendicular to a central axis of the body, the body being no larger in diameter above the first shoulder than at the first shoulder, and a second shoulder below the first shoulder, the body being no larger in diameter above the second shoulder than at the second shoulder, and a first ring and a second ring attached to the body at a front surface of, respectively, the first shoulder and the second shoulder.
In accordance with still another aspect of the present invention, a cutting tip for being attached to a cutting bit includes a base portion, a tip portion, the tip portion being generally convex in shape, and a side portion extending between the base portion and the tip portion, the side portion being generally concave in shape.
In accordance with still another aspect of the present invention, a cutting bit includes a cutting tip having a base portion, a tip portion, the tip portion being generally convex in shape, and a side portion extending between the base portion and the tip portion, the side portion being generally concave in shape and intersecting with the tip portion at a junction. The cutting bit also includes a body having a front face to which the cutting tip is attached, a bottom portion, and a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. An imaginary cone is defined by the junction and the bottom portion and the ring is disposed inside of the cone.